Many powered machines use a single power source for multiple uses. For example, a riding lawn mower may use its engine for both locomotion of the machine as well as driving an implement such as a mulcher, mower, or tiller. On a larger scale, a fire response machine may use its engine for locomotion as well as to power an auxiliary device such as a water pump. Such machines typically employ a power takeoff, or PTO, to selectively direct the engine power to the machine wheels for locomotion or to the implement, e.g., the pump. In some cases the PTO is configured to select either the locomotion function or the auxiliary device, but not both. For example, with respect to a fire response machine, the locomotion function is not needed while pumping water, e.g., when fighting a fire, and the water pumping feature is not needed while moving, e.g., while traveling to the scene of a fire.
One such PTO is referred to a driveline PTO (DPTO) or a split-shaft PTO. An example of a DPTO is shown in US Published Application 2007/0006572 to Yu et al., entitled “System and Method for Controlling an Engine Having a Power Take Off Output Device.” In general, a DPTO allows a machine transmission to deliver power to a PTO load through the machine's transmission output shaft (i.e., “pump mode”) instead of delivering power to the machine wheels (i.e., “road mode”). In the DPTO system, one output yoke of the DPTO is linked to the machine axles and another output yoke is linked to the water pump. An input yoke of the DPTO receives power from the machine engine via the machine's transmission output shaft. This type of PTO provides certain benefits over other types of PTO such as side-drive PTO's, which typically provide less power than the DPTO, and front and rear engine PTO's, which often do not fit well within the physical layout of a typical fire response machine.
Most DPTOs include a split shaft sliding collar to selectively shift between road mode and pump mode. However, essentially all planetary transmissions provide some amount of incidental or windage generated torque at the output shaft even when in neutral. Thus, the sliding collar may be “torque locked” if too much torque is present when trying to slide the collar to change modes. Moreover, when shifting from pump mode to drive mode, if the windage generated torque at the output shaft is sufficient at engine idle to spin the pump, the operator may experience gear “grinding” as the rotating collar is forced against the stationary machine drive shaft. Although it is possible to use a clutched input to the DPTO to alleviate certain of these problems, this solution is costly and introduces additional mechanical complications and failure points into the system.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the disclosure, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use within the disclosed examples, nor is it intended to indicate any element, including solving the motivating problem, to be essential in implementing the examples described herein. The full scope of the implementations and application of the examples described herein are defined by the appended claims.